(1) Field of the Invention
The present invention relates to a steering mechanism for vehicles equipped with a power steering system, and more particularly to a steering mechanism which includes a resilient element such as a torsion bar interposed in a path of torque transmission between a steering wheel and a power assisting system adapted to boost the steering reactive force in response to the vehicle speed, and in which a damper means is provided to attenuate torsional vibrations of the steering wheel due to the interposed resilient element.
(2) Description of Prior Art
In related commonly-assigned U.S. Pat. No. 4,310,063 issued Jan. 12, 1982, there is disclosed a power steering mechanism, wherein a resilient body such as a torsion bar, which is capable of torsional deformation to produce a resilient force in a rotational direction, is interposed in a path of torque transmission between a steering wheel and a power assisting system which is designed to increase the steering reactive force in proportion to the vehicle speed, thereby varying the ratio of the steering wheel turn angle to the road wheel turn angle in response to the vehicle speed. This arrangement has advantages in that a large turn angle of the road wheels can be obtained by a relatively small turn angle of the steering wheel in parking or low-speed movement of the vehicle, while the so-called over-handling of the steering wheel in high-speed running is prevented.
However, since the afore-mentioned torsion bar has particular resilient characteristics in the torsional direction and a steering wheel having a moment of inertia is attached to this torsion bar, a free vibrational system is formed so that the steering wheel will be repeatedly subject to fine vibrations whenever the steering wheel is relieved from the manual turning force of a driven position and returns to its center position, thereby giving an uncomfortable feeling to the driver. Such behavior of the steering wheel is undesirable from the standpoint of the feeling of steering because it is directly gripped by a driver who is required to concentrate on driving the vehicle.
The present invention has been provided to eliminate the above-mentioned drawback.